The applicant plans to study the region of the q14 band of chromosome 13 which may be related to the development of retinoblastoma. Since 1963, at least 37 cases of retinoblastoma have been published which have a deletion involving 13q14. This project will use two different approaches to examine the relationship between 13q14 deletion and retinoblastoma. First, the applicant will examine esterase D, whose locus is known to be in the vicinity of 13q14, in retinoblastoma patients and their relatives. Patients with a deletion of 13q14 may be detected by their half normal red cell esterase D activity. Esterase D alleles may also be traced through families with retinoblastoma, in order to determine if the gene for familial retinoblastoma is also on 13q14. Secondly, by using a combination of somatic cell hybridization and recombinant DNA technologies, the applicant hopes to isolate and clone DNA fragments from or near 13q14. These DNA fragments would be ideal for testing retinoblastoma patients for microdeletions, for searching for DNA polymorphic sites useful in genetic counseling, and for use in any future study aimed at characterizing the retinoblastoma gene itself.